Optical information medium

ABSTRACT

An optical information medium which has excellent abrasion resistance and which further exhibits sufficient smudge-proof properties is provided. The optical information medium is coated on at least one surface with a film of a silane coupling agent containing a water- or oil-repellent substituent, said silane coupling agent being represented by the following formula (1): R 1 —Si(X)(Y)(Z) wherein R 1  is the water- or oil-repellent substituent; X, Y and Z are independently a monovalent group; and at least one of X, Y and Z is a group which is capable of forming Si—O—Si bond by polycondensation with silanol group; and said medium has an underlying layer formed in contact with said silane coupling agent film, and at least the surface of said underlying layer comprises a compound having a chemical bond represented by the formula (2): M—A wherein M is a metal atom (including a semimetal), and A is a chalcogen atom selected from O, S, Se, and Te, nitrogen atom, or carbon atom.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to an optical information medium such asread only optical disk and optical recording disk.

[0003] 2. Prior Art

[0004] Optical materials most typically used for light-transmittinglayer and the like of an optical information medium are polycarbonate-and polymethyl methacrylate-based materials in view of their favorablemoldability, transparency, price, and the like. These materials,however, suffer from insufficient abrasion resistance, and their highelectric insulation invites high susceptibility for electric charge, anda large amount of dust is likely to become attached to the surface ofthe medium during their storage or use to result in errors in therecording and reading of the optical information.

[0005] A countermeasure generally taken for such problem is applicationof a transparent, scratch-resistant hard coat on the light-transmittinglayer of the medium. The process most popularly employed in such case iscoating of a curable compound having at least two polymerizablefunctional groups such as acryloyl group in the molecule on thelight-transmitting layer followed by curing with UV or other activeenergy beam to thereby form a protective layer. Although the protectivelayer formed from such UV-curable resin may be superior in abrasionresistance compared to the surface of the resin such as polycarbonate orpolymethyl methacrylate, the level of the abrasion resistance achievedis limited to a certain level and such level is not the level of thescratch resistance sufficient for use in the optical information medium.In addition, these hard coatings are provided only for the purpose ofimparting the surface with the scratch resistance, and a smudge-proofsurface which is resistant to attachment of dust or oil mist in the air,fingerprint, and the like is not expectable.

[0006] Also proposed is application of a hard coat imparted withanti-static property for prevention of dust attachment as well assufficient scratch resistance on the substrate on the side of therecording/reading beam incidence. For example, Japanese PatentApplication Laid-Open No. (JP-A) 239946/1985 and JP-A 276145/1986propose addition as an antistatic agent of a cationic amine, an anionicalkylbenzene sulfonate, a nonionic polyol, or ethylene oxide of analkylphenol, and amphoteric imidazoline or alanine metal salt. JP-A173949/1991 proposes addition of a lauryl compound, and JP-A 80267/1992proposes addition of thiocyanic acid and an anionic surfactantcontaining alkylene glycol chain. These surfactants all have smudgeproof effects for inorganic substances such as dust. These methods,however, are substantially ineffective in preventing organic smudgessuch as fingerprint and oil mist. Furthermore, the surface abrasionresistance of the light-transmitting layer in these proposals isequivalent or inferior to that of the conventional hard coats formed byusing a UV-curable resin, and the scratch resistance sufficient forpractical use is not at all realized.

[0007] A hard coat having smudge-proof properties for organiccontaminants is proposed in JP-A 110118/1998 wherein the hard coatingmaterial used has a non-crosslinked fluorosurfactant kneaded therein.The hard coat obtained by this method, however, is insufficient inwater- and oil-repellency since only a small part of the fluorocompoundis exposed to the hard coat surface. When the amount of thefluorosurfactant added to the hard coating material is increased inorder to secure sufficient water- and oil-repellent function, theresulting hard coat will suffer from reduced hardness, poor opticalproperties due to leaching of the excessive surfactant, and handlinginconvenience.

[0008] As a countermeasure for such problem, JP-A 213444/1999 proposescoating of a fluoropolymer on the surface of the conventional opticaldisk substrate comprising polycarbonate or the like, and in thisapplication, the water- and oil-repellency is imparted by coating thefluoropolymer on the resin substrate of the optical disk. In contrast tothe method wherein a lubricant or the like is kneaded in the hardcoating material, the water- and oil-repellent compound of thisapplication is exposed to the entire surface of the hard coat film andsufficient smudge-proof properties are _thereby realized. Thefluoropolymer of this method, however, suffers from extremely pooradhesion to the underlying substrate since the fluoropolymer is onlyphysically adsorbed to the underlying substrate by van der Waals force,and the surface treatment with the fluoropolymer is associated with aserious problem of poor durability. JP-A 187663/1994 proposes coating ofan acrylic resin surface with a water- and oil-repellent compound bycoupling reaction. In this method, a smudge-proof film exhibiting higheradhesion to the underlying surface compared to the JP-A 213444/1999 isprovided by coating a water- and oil-repellent compound containing silylgroup on the surface of an acrylic resin containing a hydrophilicsubstituent.

[0009] However, the acrylic resins disclosed in the JP-A 187663/1994 arerequired to contain an adequate amount of hydroxyl group in the polymerchain to thereby enable adsorption of the water- and oil-repellentcompound by coupling reaction. This inevitably results in the limitedchoice of the acrylic resin. In addition, density of the hydroxyl groupshould be increased to achieve sufficient adhesion between the hard coatsurface and the water- and oil-repellent compound, and this may resultin the reduced hardness of the hard coat. Alternatively, thehydrophilicity of the hard coat surface may be raised by high energybeam treatment such as plasma or corona discharge treatment. Suchtreatment, however, is not sufficient in effectively enabling thecoupling reaction with the water- and oil-repellent agent, and thesatisfactory adhesion is less likely to be achieved solely by thismethod.

[0010] JP-A 203726/1999 discloses a method for improving the scratchresistance of the surface of a resin light-transmitting layer. In thismethod, two or more inorganic material layers of SiN or SiO are formedby vapor deposition such as sputtering to a total thickness ofapproximately several hundred nm on the light-transmitting layercomprising a UV-curable resin. However, it is quite difficult to obtaina scratch resistance of practically acceptable level by forming aninorganic film of such thickness.

SUMMARY OF THE INVENTION

[0011] An object of the present invention is to provide an opticalinformation medium having a light-transmitting layer exhibiting highscratch resistance of practically acceptable level. Another object ofthe present invention is to provide an optical information mediumwherein the light-transmitting layer or the supporting substrate isimparted with smudge-proof properties for organic contaminants such asoil mist and fingerprint (improved readiness for removal of thecontaminant) without detracting from the scratch resistance of thelight-transmitting layer, and in other words, an optical informationmedium wherein stable recording/reading is enabled for a prolongedperiod even if the medium is used as a medium unaccommodated in acartridge, shell, or caddy, namely, with its surface exposed to contactby fingers and the like. A further object of the present invention is toimprove lubricity and durability of the surface on the side of theoptical head in a magneto-optical disk used in magnetic field modulationprocess.

[0012] In order to solve the problems as described above, the inventorsof the present invention have conducted various investigations for thesurface protective layer of the optical information medium. It was thenfound that it is effective to provide a light-transmitting layerexhibiting excellent scratch resistance comprising a resin and/or ametal (including a semimetal) compound, or hard carbon (DLC)(preferably, separately from the supporting substrate) on the surface ofthe optical information medium. It was also found that it is effectiveto provide an underlying layer (which may also function as otherconstituent member of the medium) exhibiting excellent scratchresistance on the surface of the optical information medium and tofurther apply a water- and oil-repellent film exhibiting excellentadhesion on the underlying layer.

[0013] To be more specific, the present is as described below.

[0014] (1) An optical information medium to be optically recorded and/orread, wherein

[0015] said medium is coated on at least one surface with a film of asilane coupling agent containing a water- or oil-repellent substituent,said silane coupling agent being represented by the following formula(1):

R₁—Si(X)(Y)(Z)  (1)

[0016] wherein R₁ is the water- or oil-repellent substituent; X, Y and Zare independently a monovalent group; and at least one of X, Y and Z isa group which is capable of forming Si—O—Si bond by polycondensationwith silanol group; and

[0017] said medium has an underlying layer formed in contact with saidsilane coupling agent film, and at least the surface of said underlyinglayer comprises a compound having a chemical bond represented by theformula (2):

M—A  (2)

[0018] wherein M is a metal atom (including a semimetal), and A is achalcogen atom selected from O, S, Se, and Te, nitrogen atom, or carbonatom.

[0019] (2) An optical information medium according to the above (1)wherein the surface of the underlying layer coated with said silanecoupling agent comprises an active energy beam-curable resin containinga metal (including semimetal) chalcogenide particle, and said metalchalcogenide particle has an average particle size of up to 500 nm.

[0020] (3) An optical information medium to be optically recorded and/orread, wherein

[0021] said medium is coated on at least one surface with a film of asilane coupling agent containing a water- or oil-repellent substituent,said silane coupling agent being represented by the following formula(1):

R₁—Si(X)(Y)(Z)  (1)

[0022] wherein R₁ is the water- or oil-repellent substituent; X, Y and Zare independently a monovalent group; and at least one of X, Y and Z isa group which is capable of forming Si—O—Si bond by polycondensationwith silanol group; and

[0023] said medium has an underlying layer formed in contact with saidsilane coupling agent film, and said underlying layer has a surfacecomprising a thin layer of a metal (including a semimetal) compoundhaving a thickness of up to 1 μm formed in contact with said silanecoupling agent film, and a metal (including a semimetal)compound-containing layer having a thickness thicker than said thinlayer is formed in contact with said thin layer and on the side oppositeto said silane coupling agent film.

[0024] (4) An optical information medium according to the above (3)wherein said metal (including a semimetal) compound-containing layerformed in contact with said thin layer comprises an active energybeam-curable resin containing particles of a metal compound selectedfrom a metal (including semimetal) chalcogenide, a metal (includingsemimetal) nitride, and a metal (including semimetal) carbide; and saidmetal compound particle has an average particle size of up to 500 nm.

[0025] (5) An optical information medium according to the above (3)wherein said metal (including a semimetal) compound-containing layerformed in contact with said thin layer comprises a compositioncontaining a hydrolyzable metal (including semimetal) compound.

[0026] (6) An optical information medium according to the above (3)wherein said metal (including a semimetal) compound-containing layerformed in contact with said thin layer comprises a compound containing apoylsilazane.

[0027] (7) An optical information medium according to any one of theabove (1) to (6) wherein the substituent R₁ in formula (1) is a water-or oil-repellent fluorohydrocarbon substituent.

[0028] (8) An optical information medium according to any one of theabove (1) to (7) wherein at least one of X, Y and Z in formula (1) isselected from a halogen, —OH, —OR₂ (wherein R₂ is an alkyl group),—OC(O)CH₃, —NH₂ and —N═C═O.

[0029] (9) An optical information medium according to any one of theabove (1) to (8) wherein

[0030] said medium has a supporting substrate, and the recording and/orthe reading is accomplished by irradiating a light beam from the side ofsaid supporting substrate, and

[0031] said silane coupling agent film is formed on the side of thelight beam incidence.

[0032] (10) An optical information medium according to the above (9)wherein

[0033] said optical information medium is a magneto-optical disk used bymagnetic field modulation process which has a recording layer formed onthe supporting substrate, wherein the recording and the reading isaccomplished by irradiating a light beam from the side of saidsupporting substrate, and wherein a magnetic head is run on the side ofsaid recording layer, and

[0034] said disk is coated with said silane coupling agent film on boththe side of the light beam incidence and the side of the magnetic head.

[0035] (11) An optical information medium comprising a supportingsubstrate and a film layer formed on the supporting substrate to beoptically recorded and/or read by a light beam irradiated from the sideof said supporting substrate or said film layer, wherein

[0036] said medium is coated on the side of the light incidence with athin layer having a thickness of up to 1 μm comprising a metal(including a semimetal) compound selected from a metal (includingsemimetal) chalcogenide, a metal (including semimetal) nitride, and ametal (including semimetal) carbide, and

[0037] a metal (including a semimetal) compound-containing layer havinga thickness thicker than said thin layer is formed in contact with saidthin layer and on the side opposite to the side of the light incidence.

[0038] (12) An optical information medium comprising a supportingsubstrate and a film layer formed on the supporting substrate to beoptically recorded and/or read by a light irradiated from the side ofsaid supporting substrate or said film layer, wherein

[0039] said medium is coated on the side of the light incidence with athin layer having a thickness of up to 1 μm comprising hard carbon(diamond like carbon), and

[0040] a metal (including a semimetal) compound-containing layer havinga thickness thicker than said thin layer formed in contact with saidthin layer and on the side opposite to the side of the light incidence.

[0041] (13) An optical information medium according to the above (11) or(12) wherein said metal (including a semimetal) compound-containinglayer formed in contact with said thin layer comprises an active energybeam-curable resin containing particles of a metal compound selectedfrom a metal (including semimetal) chalcogenide, a metal (includingsemimetal) nitride, and a metal (including semimetal) carbide; and saidmetal compound particle has an average particle size of up to 500 nm.

[0042] (14) An optical information medium according to the above (11) or(12) wherein said metal (including a semimetal) compound-containinglayer formed in contact with said thin layer comprises a compositioncontaining a hydrolyzable metal (including semimetal) compound.

[0043] (15) An optical information medium according to the above (11) or(12) wherein said metal (including a semimetal) compound-containinglayer formed in contact with said thin layer comprises a compoundcontaining a polysilazane.

[0044] (16) An optical information medium comprising a supportingsubstrate and a film layer formed on the supporting substrate which isoptically recorded and/or read by irradiating a light beam from the sideof said supporting substrate or said film layer, wherein

[0045] said medium is formed on the side of the light incidence with alight-transmitting layer; and at least a part of said light-transmittinglayer comprises an active energy beam-curable resin containing particlesof a metal compound selected from a metal (including semimetal)chalcogenide, a metal (including semimetal) nitride, and a metal(including semimetal) carbide; and said metal compound particle has anaverage particle size of up to 500 nm.

[0046] (17) An optical information medium according to any one of theabove (4), (13), or (16) wherein said metal compound particle is a metalchalcogenide particle.

[0047] (18) An optical information medium according to any one of theabove (2), (4), (13), or (17) wherein said metal chalcogenide particleis silica particle.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048]FIG. 1 is a cross sectional view of the optical recording mediumaccording to an embodiment of the present invention.

[0049]FIG. 2 is a cross sectional view of the optical recording mediumaccording to another embodiment of the present invention.

[0050]FIG. 3 is a graph showing alteration in the error rate beforedeposition of the fingerprint (initial) and after wiping of thefingerprint.

DETAILED DESCRIPTION OF THE INVENTION

[0051] Next, the present invention is described in detail.

[0052] The optical information medium of the present invention is coatedon at least one surface with a film of a silane coupling agentrepresented by the following formula (1) containing a water- oroil-repellent substituent. The medium has an underlying layer formed incontact with said film of silane coupling agent, and at least thesurface of said underlying layer in contact with said silane couplingagent film comprises a compound having a chemical bond represented bythe formula (2) such as Si—O bond. The film of the silane coupling agentformed is a monomolecular film or a thin film resembling a monomolecularfilm because of the chemisorption reaction mechanism, and therefore,performance of the underlying surface, namely, the surface including thechemical bond moiety represented by the formula (2) is directlyreflected to the surface of the medium with regard to hardness, scratchresistance and other mechanical properties of the medium. Accordingly,by constituting the surface of the medium as described above, aremarkable improvement in the scratch resistance of the surface of theoptical information medium as well as provision of the smudge-proofproperties without detracting from such scratch resistance are enabled.At the same time, the smudge-proof surface could be imparted with highdurability. To be more specific, the silane coupling agent undergoeschemisorption reaction with the chemical bond moiety such as Si—O bondrepresented by formula (2) in the compound contained in the mediumsurface in contact with the silane coupling agent, and therefore, thesilane coupling film firmly adheres to the underlying surface andsimultaneously exerts water- and oil-repellent function to therebyrealize the smudge-proof properties with improved readiness forcontaminant removal. Therefore, the medium does not suffer from seriouscontamination problem when it is used without being accommodated in acartridge, shell, or caddy. In addition, the underlying surfacecontaining the chemical bond moiety such as Si—O bond represented byformula (2) exhibits excellent durability as well as sufficient scratchresistance, and these properties synergistically functions with thesmudge-proof properties. These merits are also realized with no adverseeffects on other performance of the medium.

[0053] Alternatively, the medium may be provided with an underlyinglayer comprising two or more layers instead of the underlying layersurface as described above in order to improve the adhesion with thesilane coupling agent film and the scratch resistance. The underlyinglayer may comprise a thin layer (with a film thickness of up to 1 μm) ofa metal (including a semimetal) compound formed as a surface layer incontact with the silane coupling agent film, and a metal (including asemimetal) compound-containing layer formed as an inner layer in contactwith said thin layer and on the side opposite to said silane couplingagent film. In this case, the inner layer has a thickness thicker thanthe thin layer. The metal compound thin layer formed as the surfacelayer comprises a metal compound as its major component, and the thinlayer preferably comprises 90% (mass %) or more of the metal compound.

[0054] The optical information medium of the present invention comprisesa supporting substrate of a resin, glass, or the like and one ore morefilm layers at least including a recording layer or a reflective layerdisposed on the supporting layer, and the medium is recorded and/or readby irradiating the film layer with laser beam or other light.

[0055] The medium may be irradiated with the light either from the sideof the supporting substrate, or from the side of the film layer.Alternatively, the medium may further comprise a supporting substrate ora protective layer of a resin, glass, or the like disposed on the filmlayer, and the medium may be recorded and/or read by irradiating thelight beam from the surface of such layer.

[0056] The present invention is most effective when it is applied to alight-transmitting layer through which the recording/reading beam isirradiated. In the case of a magneto-optical disk of magnetic fieldmodulation type, the light beam is generally irradiated from the side ofthe supporting substrate, and the present invention is effective when itis applied to the side of the light beam incidence. The presentinvention, however, is also highly effective when it is applied to theside opposite to the light-transmitting layer since the magnetic headmoves on the side of the recording layer of the magneto-optical disk,namely, on the organic protective layer covering the recording layer,and the surface of the protective layer should have an improvedlubricity and durability.

[0057] Furthermore, when improvement in the scratch resistance and othermechanical strength of the surface of the optical information medium isthe main object, the medium may be provided at least on the side of thelight incidence with a light-transmitting layer containing at least in apart thereof an active energy beam-curable resin containing metalcompound particles such as metal (including semimetal) chalcogenideparticles (average particle size, up to 500 nm) without combining thelight-transmitting layer with the overlying film of silane couplingagent as described above. Such embodiment is also advantageous in thepresent invention. In addition, it is also effective to provide theunderlying layer comprising two or more layers such that the layercorresponding to the surface layer is arranged at least on the side ofthe light incidence, and in such a case, the layer may be formed eitherfrom the material as described above for the surface layer or hardcarbon (DLC).

[0058] Typical constitutions of the optical information medium of thepresent invention are shown in FIGS. 1 and 2.

[0059] The optical information medium shown in FIG. 1 comprises asubstrate 1, a recording layer 2 disposed on the substrate 1, and alight-transmitting layer 3 disposed on the recording layer 2. On thelight transmitting layer 3 are formed an underlying layer 4 and a silanecoupling agent film 5 in this order. The underlying layer 4 comprises aninner layer 41 on the side of the light-transmitting layer 3 and asurface layer 42 on the side of the silane coupling agent film 5. Therecording/reading laser beam enters the medium from the side of thelight-transmitting layer 3 through the silane coupling agent film 5 andthe underlying layer 4.

[0060] In the constitution of FIG. 1, various modification may be madewithin the scope of the present invention as described above. Forexample, when the silane coupling agent film 5 is provided, the silanecoupling agent film 5 may be formed by using the inner layer 41 for itsunderlying layer without providing the surface layer 42, and such innerlayer may also constitute a part or all of the light-transmitting layer3. Depending on the intended use of the medium, the medium may beprovided with no silane coupling agent film 5, and in this case, theunderlying layer 4 may serve the surface layer of the medium. The mediummay be also provided with no surface layer 42 with the inner layer 41 ofparticular composition serving as the surface layer, and such innerlayer may also constitute a part or all of the light-transmitting layer3.

[0061] On the other hand, the optical information medium shown in FIG. 2comprises a supporting substrate 1, and a recording layer 2 and aprotective layer 6 formed on the supporting substrate 1 in this order.On the supporting substrate 1 are formed an underlying layer 4 and asilane coupling agent film 5 in this order on the surface opposite tothe recording layer 2. The underlying layer 4 comprises two layers,namely an inner layer 41 on the side of the supporting substrate 1 and asurface layer 42 on the side of the silane coupling agent film 5. Therecording/reading laser beam enters the medium from the side of thesupporting substrate 1 which also serve as the light-transmitting layerthrough the silane coupling agent film 5 and the underlying layer 4.

[0062] Various modification may be made in the constitution of FIG. 2 asin the case of FIG. 1. The supporting substrate 1 and the inner layer41, however, may preferably comprise separate members.

[0063] The optical information medium of the present invention is notlimited to the embodiments shown in the drawings, and various otherembodiments are possible.

[0064] The present invention is described in further detail.

[0065] In the embodiment of the present invention wherein the medium isused in combination with the water- and oil-repellent silane couplingagent, the surface of the underlying layer which is to be covered withthe water- and oil-repellent silane coupling agent should comprise acomposition containing a compound having a chemical bond represented byformula (2) such as Si—O bond, namely, a composition containing achemical bond moiety represented by formula (2):

M—A  (2)

[0066] wherein M is a metal atom (including semimetal atom), and A is achalcogen atom selected from O, S, Se, and Te, nitrogen atom, or carbonatom.

[0067] The metal atom (including semimetal atom) represented by M shouldbe an atom which is not limited for its oxidation number in the compoundor the composition, and exemplary such atoms include Si, Ti, Al, Zn, Zr.

[0068] In order to facilitate smooth chemisorption reaction of thesilane coupling agent, the chemical bond moiety may preferably comprisea metal atom and a chalcogen atom such as oxygen. Exemplary suchchemical bonds include Si—O bond, Ti—O bond, Al—O bond, Zn—C bond, Zr—Obond, and Zn—S bond. Among these, use of a composition containing Si—Obond is most preferable in view of the wide choice of availablematerials which can be adopted in the practical use. In such a case, thecomposition containing Si—O bond may constitute the supporting substrateor the light-transmitting layer itself, or alternatively, suchcomposition may be covered over the surface of the substrate or thelight-transmitting layer which is free from such Si—O bond. In order toreliably attain sufficient scratch resistance in these embodiments, thesurface layer region of the underlying layer with a thickness of atleast 100 nm, and more preferably at least 500 nm from the surface maypreferably comprises a compound having Si—O bond. In either embodiments,incorporation of the compound having Si—O bond in the surface region ofthe underlying layer to be covered with the silane coupling agent willrealize a remarkable improvement in the adhesion of the coupling agentto the surface of the underlying layer.

[0069] The most typical composition containing the compound having Si—Obond is glass, and in the use of the glass, the entire substrate may beconstituted from the glass. Alternatively, a thin film containing SiO₂as its main component may be formed on a resin by means of sputtering orthe like. Further possible embodiments are use of a resin such aspolydimethylsiloxane which contains siloxane bond in its molecularchain, and employment of a process wherein a coupling agent such as analkoxysilane is coated on a resin. In a still further embodiment, athermoplastic resin such as polycarbonate or polymethyl methacrylate oran active energy beam-curable resin having admixed therein silicaparticles may be used, and when a composition having the silicaparticles dispersed is used for the light-transmitting layer, the silicaparticles may preferably have an average particle diameter of up to 500nm, and more preferably, up to 100 nm. When the particle diameter is inexcess of 500 nm, the diameter will be very close to or in excess of thewavelength of the recording/reading beam most widely used in an opticalinformation medium, and adverse effects are induced in the recorded oroutput signal. Although no particular lower limit is set for theparticle size, the lower limit is typically about 5 nm.

[0070] Among the compositions containing a compound having Si—O bond asdescribed above, use of an active energy beam-curable resin admixed withsilica particles for the underlying layer to be covered with the water-and oil-repellent silane coupling agent is most preferable inconsideration of its use for the optical information medium. In such acase, a conventional resin such as polycarbonate or polymethylmethacrylate which has advantageous workability and cost effectivenessin the form of a substrate or a sheet may be overlaid with theunderlying layer comprising a coating of an active energy beam-curableresin admixed with silica particles, and use of such product for theunderlying layer is preferable. This facilitates convenient formation ofthe light-transmitting layer having extremely high durability.

[0071] The active energy beam-curable resin admixed with silicaparticles used may be a resin composition having silica particles simplydispersed therein. However, it is preferable that the silica particles(preferably having a particle size as described above) are chemicallybonded to the polymer chain since fixture of the silica particles to thepolymer chain by chemical bonding invites increase in the surfacehardness of the cured film. The silica particles may be chemicallybonded to the polymer chain after the curing, for example, by the methodproposed in JP-A 100111/1997.

[0072] The active energy beam-curable resin admixed with the silicaparticles may typically comprise a UV-curable resin, and an exemplaryUV-curable resin wherein the silica particles are fixedly bonded is theresin commercially available under the trade name of DeSolite Z7501(manufactured by JSR Co., Ltd.).

[0073] The underlying layer as described above may be thelight-transmitting layer, the supporting substrate, or other memberconstituting the optical information medium, or alternatively, theunderlying layer may be a layer covering the member constituting theoptical information medium. In either case, the underlying layer mayhave a thickness of about 0.1 μm to about 1.5 mm.

[0074] The content of the Si—O bond in the underlying layer ispreferably at least 15%, and more preferably at least 20% in mass %.When the content is excessively low, the abrasion resistance of theunderlying layer will not be sufficiently improved and the adhesion tothe silane coupling agent will also be insufficient to detract from themerits of the present invention.

[0075] The active energy beam-curable resin admixed with the silicaparticles is typically in the form of a dilution with an organic solventbecause of its production process and for the purpose of reliablyattaining the product stability. Accordingly, when the underlying layeris formed by using such material, the organic solvent should be removedto a sufficient level before the irradiation of the active energy beam.Typically, the preferable content of the organic solvent in theunderlying layer is preferably up to 5% (mass %).

[0076] The organic solvent may be removed by heating. However, when theunderlying layer is formed by spin coating, the removal of the organicsolvent may be accomplished simultaneously with the coating of thecoating solution by spinning off the coating solution at a high speedfor a relatively long period. Removal of the solvent simultaneously withthe spin coating is preferable in view of improving the productivity.However, in view of improving the surface hardness and reliability ofthe underlying layer, removal of the solvent by such means as heatdrying is preferable since the underlying layer can be provided withdensity gradient of the silica particles in the vertical direction ofthe layer by heat treating the coated film of the underlying layerbefore its curing.

[0077] When a thin film is formed by coating a liquid mixture or asolution of two or more components having relatively low mutualcompatibility or affinity, it is known that each component generallyundergoes self-assembly when the film is left at a high temperature fora prolonged period. Such tendency was also confirmed for the UV-curableresin admixed with the silica particles as described above in theinvestigation conducted by the inventors of the present invention, andto be more specific, the monomer and the like which are the organiccomponents and the silica particle which is an inorganic componentrespectively exhibited tendency to undergo self-assembly when the resinwas set at a relatively high temperature for a prolonged period beforethe UV irradiation. In the present invention, the underlying layer istypically formed on the surface of a resin material layer such as thelight-transmitting layer and the supporting substrate, and byexperiencing the setting, the organic components in the UV-curable resintend to undergo self-assembly near the boundary with thelight-transmitting layer or the supporting substrate formed from a resinexhibiting high affinity for the organic components, while the inorganicsilica particles tend to undergo self assembly at the surface of theunderlying layer. In other words, the silica particles are distributedwith a density gradient in the vertical direction of the underlyinglayer, and the surface of the underlying layer exhibits an improvedhardness compared to the case where no density gradient is formed. Atthe same time, the underlying layer exhibits an elastic modulus whichgradually decreases from the surface of the underlying layer to the sideof the light-transmitting layer or the supporting substrate.Accordingly, drastic change in the elastic modulus, thermal expansioncoefficient, and other physical properties at the boundary between thelight-transmitting layer or the supporting substrate and the underlyinglayer is mitigated compared to the case wherein no density gradient ispresent. As a consequence, distortion of the disk which has beenintentionally or unintentionally applied to the disk as well as internalstress resulting from rapid change in the exterior temperature aregradually alleviated near the boundary between the light-transmittinglayer or the supporting substrate and the underlying layer. Therefore,occurrence of cracks on the surface of the underlying layer induced bysuch mechanical or thermal impact is highly suppressed.

[0078] It should be noted that the process which may be employed forcreating the density gradient of the silica particles in the underlyinglayer having the silica particles dispersed therein is not limited tothe heat drying as described above, and any process may be adopted aslong as the desired density gradient can be realized. It should also benoted that density gradient can also be created for a resin materialfree from the non-reactive organic solvent by such means as heattreatment before the curing.

[0079] For the purpose of confirming whether the density gradient of thesilica particles has been really created in the resulting underlyinglayer, various analysis known in the art may be employed including X-rayphotoelectron spectroscopy (XPS) which is a common method used in thesurface elementary analysis. To find out the detailed distribution ofthe silica density in vertical direction of the underlying layer, thesurface analysis is preferably employed in combination with etching byion beam sputtering. Alternatively, a cross section of the underlyinglayer may prepared, and the exposed section may be observed by variouselementary analysis methods. Inmost cases, however, confirmation of thedifference in the surface silica density in relative comparison betweenthe underlying layers formed under different heat drying and otherconditions is sufficient, and etching in the vertical direction and theobservation of the cross section are usually not required.

[0080] The desirable range of the density gradient of the silicaparticles can not be defined to a particular range since various factorsincluding content of the silica particles in the resin, thickness of theas-deposited underlying layer, physical properties of the material usedin the light-transmitting layer or the supporting substrate on which theunderlying layer is formed, and surface hardness and reliabilityrequired are inseparably intertwined. Therefore, the optimal silicadensity gradient should be empirically determined by trial and error,for example, by altering the heat drying condition in the course of thefilm formation.

[0081] The presence of the silica particle density gradient is notnecessarily a prerequisite in the formation of the underlying layerusing the UV-curable resin having the silica particles admixed therein.As described above, provision of the density gradient may be adequatelydetermined by taking the balance between the improvement of the hardnessand reliability realized by the development of the density gradient andthe productivity into consideration.

[0082] The present invention has been described by featuring silicawhich is the most preferred among the compounds having the chemical bondrepresented by formula (2). However, what has been described in theforegoing applies to all of the metal chalcogenides which are preferablefor use in the present invention, and to the metal nitrides (e.g.silicon nitride) and the metal carbides (e.g. silicon carbide andcalcium carbide) which are also the compounds having the chemical bondrepresented by formula (2).

[0083] The underlying layer as described above may also comprise two ormore layers in order to improve the adhesion between the water- andoil-repellent silane coupling agent film and the underlying layer or tofurther improve scratch resistance of the surface of thelight-transmitting layer. To be more specific, a thin film may be formedas the surface layer by vapor deposition such as sputtering,evaporation, ion plating, or CVD on the surface of the lighttransmitting layer and in contact with the silane coupling agent, and aninner layer containing a metal compound and having a compositiondifferent from that of the thin layer may be formed in contact with thethin layer and on the side nearer to the recording layer so that theunderlying layer is constituted from the surface layer and the innerlayer.

[0084] In a typical embodiment, the layer comprising an active energybeam-curable resin containing silica particles as described above may becoated as the inner layer on the surface of the light-transmitting layeror the recording layer, and after an optional surface modificationtreatment, the thin layer may be formed as the surface layer on theinner layer by sputtering using a SiO₂ target. The water- andoil-repellent silane coupling agent film may be thereafter formed on thesurface layer.

[0085] The surface layer may be formed to a thickness of up to 1 μm, andpreferably to a thickness in the range of 10 nm to 1 μm, and morepreferably to 20 nm to 500 nm. When the thickness is in excess of 1 μm,the surface layer or the inner layer will suffer from the risk of crackdevelopment. When the surface layer is too thin, no substantialimprovement in the scratch resistance will be realized over theembodiment wherein no surface layer is formed.

[0086] Exemplary materials favorably used in the formation of thesurface layer include silicon oxide, titanium oxide, aluminum oxide,zirconium oxide, silicon nitride, titanium nitride, silicon carbide, andcalcium carbide.

[0087] On the other hand, the inner layer may comprise an active energybeam-curable resin containing silica particles as described above, andalternatively, a composition containing a hydrolyzable metal compound.Such film may be formed, for example, by sol-gel process from a solutioncontaining a hydrolyzate prepared by adding an inorganic acid such ashydrochloric acid or sulfuric acid or an organic acid such as aceticacid to an organosilicon compound such as a tetraalkoxysilane, and acuring catalyst such as acetyl acetonate complex or perchlorate.

[0088] The inner layer may also comprise a material containing apolysilazane or a silica component derived from a polysilazane. Apolysilazane is generally known to be hydrolyzed by the moisture in theair when it is heated in air to form high purity silica. The compoundsgenerally referred as “polysilazane” in the present invention arecompounds of low molecular weight to high molecular weight havingSi—N—Si bond. Exemplary such polysilazanes include cyclic inorganicpolysilazanes having a structure represented by formula(—Si(H)₂—NH—)_(n) wherein n is 100 to 50000; a chain inorganicpolysilazanes and mixtures thereof; and polyorganohydrosilazanes whereinthe hydrogen atoms binding to the silicon atoms of an inorganicpolysilazane are partly or entirely replaced with an organic group. Theinner layer may also comprise a polysiloxazane wherein oxygen has beenincorporated in the molecule, a polymetallosilazane prepared by reactingwith a metal alkoxide; or a polyborosilazane prepared by reacting withan organic boron compound.

[0089] In contrast to the surface layer, the inner layer may preferablycontain an organic component in addition to the inorganic component.With regard to the composition as described above, the composition maycontain an active energy beam-curable resin containing silica particles,and alternatively, a silicon compound formed from an alkoxysilane orpolysilazane by using a material wherein the silicon atom has an organicsubstituent such as a long chain hydrocarbon group for the material tobe cured.

[0090] By using such composition including both inorganic and organiccomponents for the inner layer, not only the strong adhesion between theinner layer and the surface layer, but also an equivalently improvedadhesion between the inner layer and the light-transmitting resin layerare realized. It should be noted that, in the present invention, the“composition including both inorganic and organic components” may be amixture of the inorganic and the organic compounds, or a substancewherein an inorganic bond such as Si—O—Si and an organic substituentsuch as Si—R (wherein R is a hydrocarbon group or the like) are presentin a polymeric compound. Both are within the scope of the presentinvention.

[0091] When a resin light-transmitting layer is disposed between theinner layer and the recording layer, the constitution of the medium willbe such that an intermediate layer is formed between thelight-transmitting layer and the surface layer, and the high risk ofcrack development found in the case when a thin layer solely consistingan inorganic material is formed on the resin light-transmitting layercan be suppressed. Such effect is attained since the drastic differencein elastic modulus and thermal expansion coefficient at the boundarybetween the resin light-transmitting layer and the inorganic thin layeris moderated by the material inserted between these layers, namely, bythe material containing both the organic and the inorganic content.

[0092] The inner layer is preferably deposited to a thickness more thanthat of the surface layer. To be more specific, the inner layer maypreferably have a thickness which is about 1.5 to 50 folds thicker thanthat of the surface layer, and preferably, to a thickness of 0.1 μm ormore, and more preferably to a thickness of 0.2 μm or more. There is noparticular upper limit for the thickness of the inner layer. The upperlimit, however, is generally around 30 μm.

[0093] JP-A 203726/1999 discloses a method wherein surface scratchresistance is improved by providing two or more thin layers comprisingan inorganic compound on a resin light-transmitting layer. In the methodproposed in this patent application, two or more inorganic materiallayers of SiN or SiO are formed on the surface of the resinlight-transmitting layer comprising a UV-curable resin by vapordeposition such as sputtering to a thickness of approximately severalhundred nm. There is described in JP-A 203726/1999 that a surfaceexhibiting improved scratch resistance is obtained by such constitution.

[0094] However, it is quite difficult to obtain a scratch resistance ofpractically acceptable level by forming an inorganic film of suchthickness. As a matter of fact, the evaluation conducted in the Exampleof JP-A 203726/1999 is the evaluation of microhardness which is unlikelyto reflect the hardness of the underlying resin layer, and no evaluationunder the conditions resembling the environment of practical use, forexample, evaluation of abrasion resistance or steel wool test, areconducted. In addition, in the method of JP-A 203726/1999, a layersolely comprising an inorganic compound is formed directly on the layerof the UV curable resin which is an organic compound, and it can not beassumed that a sufficient adhesion is realized between the inorganicmaterial layer and the UV-curable resin layer. Accordingly, peeling ofthe inorganic layer and cracks are expected to occur when such opticaldisk is left under high temperature conditions.

[0095] It should be noted that, when the underlying layer is constitutedin the present invention from the two or more layers as described above,the underlying layer may also be the light-transmitting layer, thesupporting substrate, or other member constituting the opticalinformation medium, or alternatively, the underlying layer may be alayer covering the member constituting the optical information medium.

[0096] The embodiment of the present invention wherein the underlyinglayer comprises two or more layers has been described in the foregoingfor the case wherein a film of water- and oil-repellent silane couplingagent is formed on the underlying layer. However, when the primaryobject is improvement of scratch resistance of the surface of theoptical information medium, the medium may be provided solely with theinner layer and the surface layer without combining these layers withthe silane coupling agent film.

[0097] In the embodiment wherein no silane coupling agent film isprovided on the surface of the light-transmitting layer, the surfacelayer may be constituted from a thin layer of hard carbon (Diamond LikeCarbon, DLC) since there is no need to take the chemical reactionbetween the coupling agent and the surface layer into consideration. TheDLC thin layer can be formed by techniques commonly employed in the art,for example, by sputtering or CVD to a thickness equivalent to thesurface layer as described above. The DLC thin film may preferably havea Vickers hardness Hv of at least 13.

[0098] In addition, when water and oil repellency is not particularlyrequired for the surface of the light-transmitting layer and an extremeimprovement in the scratch resistance of the light-transmitting layer isnot demanded, an embodiment wherein the surface of thelight-transmitting layer is formed from a single layer of metal(including a semimetal) compound is also effective. A necessary andsufficient scratch resistance of practically acceptable level is quiteoften realized by such single layer constitution in the case of someread only-type mediums although the situation may greatly vary dependingon the intended use and recording density of the particular opticalinformation medium.

[0099] In such embodiment, the medium is most preferably provided with alight-transmitting layer which contains an active energy beam-curableresin admixed with particles of a metal compound at least in some partsthereof (and preferably, in its surface layer region) The metal compoundis selected from the metal chalcogenide, metal nitride, and metalcarbides as described above, and preferably, the metal compound isparticles of a metal chalcogenide (most preferably silica particles).The term “single layer constitution” is used in this context to describethe situation that the metal compound-containing layer comprises onesingle layer, and not the situation that the entire light transmittinglayer comprises one single layer. For example, an embodiment wherein thesurface of the resin supporting substrate is covered with the layer ofan active energy beam-curable resin containing silica particles iswithin the scope of such constitution, and such embodiment is quitepreferable. Provision of the silica particle-containing layer separatelyfrom the resin supporting substrate may be even more advantageouscompared to the use of a resin supporting substrate having the particleskneaded therein since such separate provision is free from the problemsassociated with the particle-containing supporting substrate, forexample, the problems of increased thickness of the resin supportingsubstrate and the resulting loss of design choice in the thickness, andcomplicated production steps due to the necessity of the particleincorporation which avoids use of conventional resin molding processes.

[0100] It is typical that each of the surface layer and the inner layerare formed from one single layer. These layers, however, may be formedfrom two or more layers if necessary, and in such a case, the totalthickness of these layers should be controlled to fall within thethickness range as described above.

[0101] In the present invention, the water- and oil-repellent silanecoupling agent employed in the embodiment wherein the water- andoil-repellent silane coupling agent is used in combination with theunderlying layer is the one represented by formula (1):

R₁—Si(X)(Y)(Z)  (1)

[0102] wherein R₁ is substituent having water- or oil-repellency; X, Yand Z are respectively a monovalent group; and wherein at least one ofX, Y and Z is a substituent which is capable of forming Si—O—Si bond bypolycondensation with silanol (Si—OH) group. Such substituent which iscapable of undergoing polycondensation with the silanol group may be amember selected from a halogen, —OH, —OR₂ (wherein R₂ is an alkylgroup), —OC(O)CH₃, —NH₂ and —N═C═O.

[0103] In the water- and oil-repellent silane coupling agent representedby formula (1), the substituent having water- or oil-repellencyrepresented by R₁ is a substituent whose incorporation in the compoundresults in the development of water repellency or oil-repellency of thecompound. The water repellency and the oil-repellency may be directlyrepresented by critical surface tension (γ_(c)/mNm⁻¹) which is an indexfor the surface free energy of the substance. The critical surfacetension can be calculated from the measurements of the contact angle,and to be more specific, by measuring several saturated hydrocarbonliquids (surface tension: γ₁/mNm⁻¹) each having known surface tensionfor their contact angle (θ/rad) on a smooth surface of the substance;and plotting cosθ in relation to γ₁ and extrapolating to cosθ=1 to findthe corresponding value γ_(c). When a particular substance should repela liquid, the γ_(c) of the substance should be lower than the surfacetension γ₁ of the liquid. For example, a substance having the surfacecomposition comprising methylene chain (e.g. —CH₂—CH₂—) has a γ_(c) of31 mNm⁻¹, and this substance repels water whose γ₁ at a temperature of20° C. is 73 mNm⁻¹ while it is fully wetted by n-hexadecane whose γ₁ is28 mNm⁻¹ and the contact angle becomes 0 degrees. It is an object of thepresent invention to provide a medium with water- and oil-repellencywhich is higher than that of conventional universal resins such aspolycarbonate and polymethyl methacrylate, and therefore, the criticalsurface tension γ_(c) is preferably up to 30 mNm⁻¹. Furthermore, theγ_(c) is preferably up to 25 mNm⁻¹ to enable development of thesmudge-proof performance of practically acceptable level. Although noparticular lower limit is set for the γ_(c), the lower limit of theγ_(c) is typically 6 mNm⁻¹.

[0104] The water- and oil-repellent group represented by R₁ may bepreferably a group containing a fluorohydrocarbon group, and exemplaryfluorohydrocarbon groups include a fluoroalkyl group and a fluoroalkylgroup containing a fluoroalkyleneoxy group. The fluorohydrocarbon grouppreferably contains 1 to 1000 carbon atoms in total, and thefluorohydrocarbon group may be either a straight chain group or abranched group, the straight chain group being preferable.

[0105] Exemplary fluorohydrocarbon groups include fluorinated polyolefinsegments represented by the following formulae (3) and (4) and thefluorinated polyether segments represented by the following formulae (5)and (6).

CF₃(CF₂)_(x)CH₂CH₂—  (3)

(CF₃)₂CF(CF₂)_(x)CH₂CH₂—  (4)

CF₃[OCF(CF₃)CF₂]_(x)(OCF₂)_(y)—  (5)

CF₃(OC₂F₄)_(x)(OCF₂)_(y)—  (6)

[0106] x and y in the formulae (3) to (6) are respectively a positiveinteger, and preferably a positive integer in the range of 0 to 200since no substantial improvement in the water- and oil-repellentproperties are realized by increasing the x and y beyond 200 while filmformation is impaired by the decrease of solubility in various solvents.

[0107] These groups exhibit excellent water- and oil-repellency, andamong these, the groups having a long carbon chain with no branchedstructure exhibit more preferable water- and oil-repellency.

[0108] On the other hand, the reactive groups in the silane couplingagent, namely, X, Y, and Z in Si(X)(Y)(Z) of formula (1) may be asubstituent which is capable of forming Si—O—Si bond by polycondensationwith silanol group, and such group may be selected from a halogen, —OH(hydroxy), —OR₂ (alkoxy), —OC(O)CH₃ (acetoxy), —NH₂ (amino), and —N═C═O(isocyanate). The halogen is preferably Cl or Br. In the —OR₂, R₂ is analkyl group containing 1 to 5 carbon atoms in total which may be eithera straight chain group or a branched group. R₂ may have a substituentwhich does not inhibit the chemisorption reaction while a substituentsuch as a halogen is not preferable for the same reason. Examples of the—OR₂ include methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy,and t-butoxy.

[0109] X, Y, and Z maybe the same or different, and when different, X,Y, and Z maybe different halogens or different alkoxy groups, oralternatively, X, Y, and Z may be a combination two or three types ofhalogen, hydroxy, alkoxy, acetoxy, amino, and isocyanate. In addition,it is not necessary that all of the X, Y, and Z are reactivesubstituents as long as at least one of the X, Y, and Z is a groupgenerated by hydrolysis of, for example, the halogen, alkoxy, hydroxy,acetoxy, amino, or isocyanate as described above. However, it ispreferable that all of the X, Y, and Z are the reactive groups asdescribed above in order to form a strong siloxane bond network. When X,Y, and Z are a monovalent group which is not the reactive group asdescribed above, such monovalent group may be hydrogen atom, an alkylgroup containing 1 to 5 carbon atoms, or the like.

[0110] When X, Y, and Z are a halogen, an alkoxy group, an acetoxy groupor an amino group, it is generally preferable that hydrolysis ispreliminarily promoted to some extent for conversion into silanol group.On the other hand, such preliminary hydrolysis is unnecessary when X, Y,and Z are silyl isocyanate. The silanol group and the silyl isocyanategroup smoothly undergo the coupling reaction at room temperature, and nospecial heating is required for the promotion of the reaction.Therefore, a silane isocyanate coupling agent can be used when there issome risk of deterioration of the resin or the recording layer by heat.

[0111] An example of such silane coupling agents is a productcommercially available under the trade name of DSX (manufactured byDaikin Industries, Ltd.).

[0112] The method for coating the silane coupling agent as describedabove may be adequately selected from conventional methods used in thinfilm formation. Exemplary such coating methods include spin coating, dipcoating, and spray coating, and the silane coupling agent may be coatedby any method known in the art. In addition, the silane coupling agentused for the film formation may be diluted with a solvent before its useif such dilution is necessary.

[0113] In addition, in order to improve the adhesion between theunderlying layer containing the compound having the Si—O bond or thelike as described above and the silane coupling agent, hydrophilicity ofthe surface of the underlying layer in the disk or the like may beincreased by a treating the surface with a high energy beam, forexample, by treating with ultraviolet ray, plasma, electron beam, andcorona discharge. Such surface activation using the high energy beamtreatment does not achieve sufficient effects when used for a surfacecomprising an organic-based material. However, when such treatment isapplied to the underlying layer of the composition containing a compoundhaving the Si—O bond or the like as described above, such treatment isquite effective since Si—O—Si bond and the like will be cleaved toproduce a reactive group such as Si—OH.

[0114] Such film of the silane coupling agent has a thicknesscorresponding the thickness of a monomolecular film or a ultrathin filmresembling a monomolecular film, and to be more specific, a thickness ofabout 1 to about 20 nm.

EXAMPLES

[0115] Next, the present invention is described in further detail byreferring to Examples which by no means limit the scope of the presentinvention. Comparative Examples are also described.

Example 1

[0116] Determination of Optimal Conditions For Heat Drying the CoatingFormed From a Silica Particle-admixed UV-curable Resin Diluted With anOrganic Solvent

[0117] Optimal heat drying conditions were investigated for a filmformed by using DeSolite Z7503 (manufactured by JSR Co., Ltd., silicaparticle-fixed type) as the silica particle-admixed UV-curable resin.This silica particle-admixed UV-curable resin contains propylene glycolmonomethylether acetate (PGMEA) and methyl ethyl ketone (MEK) at avolume ratio of 9:1 as dilution solvents. This product was used as thecoating solution with no further dilution. The solid content, namely,the concentration of the involatile components other than the dilutionsolvent in the total coating solution was 60% (mass %). The silicaparticles in the resin had an average particle size of about 10 nm, andthe content of the silica particles in the resin was 38% (mass %).

[0118] A polycarbonate substrate having a diameter of 120 mm and athickness of 0.6 mm was spin coated with a UV-curable resin admixed withsilica particles (DeSolite Z7503 manufactured by JSR Co., Ltd.) byspinning the resin off the disk at 6000 rpm for 2 seconds. The coatedfilm was heat-dried in air at 60° C. for 3 minutes, and cured by UVirradiation (high pressure mercury lamp, 550 mJ/cm²). The cured film hada thickness of about 3.4 μm.

[0119] Several samples were prepared by repeating the procedure asdescribed above by using different drying temperature and the dryingtime. In all samples, the cured film had substantially same thickness ofabout 3.4 μm.

[0120] On the other hand, samples not experiencing the heat drying stepwere prepared by changing the spin coating conditions from “6000 rpm for2 seconds” as described above to 6000 rpm for 60 seconds, and UV curingthe coating immediately after the spin coating with no step of heatdrying. Samples were also prepared in similar manner by using differentspin-off time in the spin coating. It should be noted that the filmprepared by adopting different spin-off time had the substantially samethickness of about 3.4 μm as long as the spin-off time was 2 seconds ormore.

[0121] Several samples were selected from the samples which had beenproduced under different film-forming conditions, and these samples wereevaluated by gas chromatography for the quantity of solvent remaining inthe film, and by X-ray fluorescence analysis for the silicon atomdensity on the film surface. The results of the measurement are shown inTables 1 and 2. TABLE 1 Total Spin coating Amount of Amount of amount ofconditions Heat drying residual residual residual Rotation conditionsPGMEA MEK solvents speed/time Temp./time (mass %) (mass %) (mass %) 6000rpm/2 sec. 60° C./3 min. 2.43% 0.55% 2.98% 6000 rpm/10 sec. None 2.93%0.78% 3.71% 6000 rpm/30 sec. None 1.58% 0.66% 2.24% 6000 rpm/60 sec.None 0.50% 0.64% 1.14%

[0122] TABLE 2 Spin coating Heat drying conditions conditions Siintensity Rotation speed/time Temp./time (kcps) 6000 rpm/2 sec. Roomtemp./1 min. 198.70 Room temp./3 min. 197.45 40° C./1 min. 197.18 40°C./3 min. 198.22 60° C./1 min. 198.10 60° C./3 min. 201.72 80° C./1 min.200.63 80° C./3 min. 204.23 6000 rpm/60 sec. None 193.59

[0123] Next, main samples of the samples as described above wereevaluated by Taber abrasion test under the following conditions. Theabrasion wheel used was CS-10F, and the haze value (ΔHaze (%)) afterabrasion of 500 rotations under the load of 4.9 N was measured. The hazevalue was measured by a fully automatic haze meter TC-HIIIDPKmanufactured by Tokyo Denshoku Gijutsu Center. Several samples of thesamples as described above were evaluated for their reliability bythermal shock test under the test conditions of: temperature of thehigh-temperature room/time of 70° C./30 minutes, and temperature of thelow-temperature room/time of −20° C./30 minutes. Occurrence of cracks inthe film was visually confirmed after repeating 100 quenching cycles asdescribed above. The results are shown in Table 3. TABLE 3 Spin coatingΔHaze (%) Crack conditions Heat drying after after Rotation conditionsabrasion thermal speed/time Temp./time test shock test 6000 rpm/2 sec.Room temp./1 min. — Yes Room temp./3 min. 6.9 Yes 40° C./1 min. — Yes40° C./3 min. — Yes 60° C./1 min. — Yes 60° C./3 min. 5.7 No 80° C./1min. 5.8 No 80° C./3 min. 6.2 No 6000 rpm/60 sec. None 13.0  Yes

[0124] The results indicate that the abrasion resistance of theunderlying layer reached sufficient level by the drying at roomtemperature of about 3 minutes. However, reliability of the cured filmwas still insufficient under such drying conditions, and the dryingtemperature and time of 60° C. for at least 3 minutes are required toprovide sufficient reliability with the film, and in particular,sufficient crack resistance with the film. On the other hand, theresults shown in Table 1 indicate that the amount of residual solvent inthe film is smaller even if no heat drying was conducted when the spincoating was conducted by spinning off at 6000 rpm for at least 30seconds compared to the case wherein the heat drying was conducted at60° C. for 3 minutes. This confirms that the insufficient of theabrasion resistance and the reliability after drying under theconditions milder than the drying at 60° C. for 3 minutes is not due tothe remaining of the organic solvent in the film but because of theinsufficient density gradient of the silica particles in the film.

[0125] As a matter of fact, Table 2 shows that a significantly higher Siintensity is detected when the heat drying is conducted under theconditions severer than 60° C. for 3 minutes compared to other samples.This strongly indicates that the density gradient of the silicaparticles is caused by self-assembly of the silica to the film surface,and the internal stress created by the repeated thermal shock cycles isrelieved by such density gradient. Accordingly, in the following part ofthe Examples, the optimal heat drying condition in forming theunderlying layer from the UV-curable resin admixed with silica particleswas assumed to be drying at 60° C. for 3 minutes.

[0126] Evaluation of the Underlying Layer

[0127] A polycarbonate substrate having a diameter of 120 mm and athickness of 0.6 mm was spin coated with a UV-curable resin admixed withsilica particles (DeSolite z7503 manufactured by JSR Co., Ltd., silicaparticle-fixed type). The coated film was heated in air at 60° C. for 3minutes for solvent removal, and cured by UV irradiation (high pressuremercury lamp, 550 mJ/cm²). The cured film had a thickness of about 3.4μm (Substrate 1).

[0128] Next, thus treated surface was evaluated for its abrasionresistance by Taber abrasion test using the same abrasion wheel and theload conditions as described above. The haze value (ΔHaze) after 100abrasion rotations was measured to be 2.0%. The substrate was placed onthe abrasion tester again to continue the evaluation. The haze value(ΔHaze) after 500 abrasion rotations in total was measured to be 5.3%.These results demonstrate the extremely high scratch resistance of thesurface. The treated surface was also evaluated for contact angle withwater at 20° C. and 60% RH using a contact angle meter (CA-Dmanufactured by Kyowa Interface Science Co., Ltd.). The contact anglewas 72.5 degrees.

Comparative Example 1

[0129] A polycarbonate substrate having a diameter of 120 mm and athickness of 0.6 mm was spin coated with a UV-curable acrylic resin(HOD-3091 manufactured by Nippon Kayaku Co., Ltd.) by spin coating, andthe coated film was cured by UV irradiation (high pressure mercury lamp,550 mJ/cm²). The cured film had a thickness of about 3.3 μm (Substrate2).

[0130] The substrate was evaluated by Taber abrasion test by repeatingthe procedure of Example 1. The haze values after 100 abrasion rotationsand 500 abrasion rotations were 14.0% and 36.2%, respectively, and thisscratch resistance was markedly inferior to that of Examples 1. Thetreated surface was also evaluated for its contact angle with water byrepeating the procedure of Example 1, and the contact angle with waterwas 97.7 degrees. On the other hand, the contact angle with n-octane ofthe treated surface was measured to be 0 degrees. Accordingly, the hardcoat treatment using the conventional UV-curable resin was capable ofimparting the surface with a certain degree of water repellency while itfailed to impart the oil repellency, and it was then estimated that suchtreatment is incapable of imparting the surface with resistance toorganic contaminants such as fingerprint.

Example 2

[0131] The surface of the substrate 1 which had been subjected to thehard coat treatment was spin coated with 0.1% (mass %) perfluorohexanesolution of DSX (manufactured by Daikin Industries, Ltd.) which is awater- and oil-repellent silane coupling agent within the scope offormula (1), and the sample was heated in air at 60° C. for 10 hours forchemisorption (Substrate 3). The film of the silane coupling agent had athickness of about 10 nm.

[0132] The thus treated substrate 3 was measured for its contact anglewith water by repeating the procedure of Example 1. The contact anglewith water was 114.0 degrees indicating a remarkable improvement in thewater repellency compared to the substrate 1 before the treatment usingthe coupling agent.

[0133] The surface of the substrate was also measured for its contactangle with n-octane by repeating the procedure as described above, andthe contact angle with n-octane was 47.2 while the contact angle withn-hexadecane was measured to be 63.8 degrees. The treated surface ofthis Example thereby confirmed to exhibit not only the water repellencybut also oil repellency, and to be highly resistant to organiccontaminants such as fingerprint. The substrate surface had a criticalsurface tension γ_(c) of 12 mNm⁻¹.

[0134] Next, the treated surface was evaluated for contact angle withwater after rubbing the surface with Bemcot Lint Free CT-8 (manufacturedby Asahi Chemical Industry Co., Ltd.) under the load of 4.9N for 300reciprocations. The contact angle with water measured was 112.0 degrees.The critical surface tension γ_(c) of the substrate surface wassubstantially equivalent to the value before the rubbing. It was thenconfirmed that the water repellency of the surface was maintained at ahigh level, and that the water- and oil-repellent coupling agent hadhigh adhesion to the surface of the underlying layer.

Comparative Example 2

[0135] The surface of the hard coat-treated substrate 2 was spin coatedwith 0.1% (mass %) perfluorohexane solution of DSX (manufactured byDaikin Industries, Ltd.) which is a water- and oil-repellent silanecoupling agent within the scope of formula (1), and the sample was heatcured in air at 60° C. for 10 hours (Substrate 4). The film of thesilane coupling agent had a thickness of about 10 nm.

[0136] The treated surface was evaluated for contact angle with water byrepeating the procedure of Example 1, and the contact angle with waterwas measured to be 111.2 degrees.

[0137] Next, the treated surface was evaluated for contact angle withwater by repeating the procedure of Example 1 after rubbing the surfacewith Bemcot Lint Free CT-8 (manufactured by Asahi Chemical Industry Co.,Ltd.) under the load of 4.9N for 300 reciprocations. The contact anglemeasured was as low as 100.7 degrees which is substantially equivalentto the contact angle with water of the substrate 2 before the coating ofthe silane coupling agent. It was then confirmed that the silanecoupling agent is little left on the surface, and the adhesion anddurability were inferior to those of Example 1. In this case, thesubstrate surface had a critical surface tension γ_(c) of 35 mNm⁻¹,which was substantially equivalent to that of the UV curable acryl resinsurface of the substrate 2 (Comparative Example 1).

[0138] As described above, in the case of the substrate treated inaccordance with the present invention, the surface of thelight-transmitting layer exhibits excellent scratch resistance, and whena film layer of a water- and oil-repellent coupling agent is formed onits surface, adhesion of this film to the light-transmitting layer isquite strong. Therefore, the favorable properties of the silane couplingagent film is maintained at the initial favorable level. In addition,even when the silane coupling agent film was formed on the surface, thefilm formed is either a monomolecular layer or a thin film resemblingthe monomolecular layer, and the favorable durability of the hardcoat-treated surface is fully reflected. As a consequence, the resultingproduct has excellent properties including the combination of thesmudge-proof properties of the coupling agent film and the abrasionresistance of the hard coat-treated surface.

[0139] The contact angle of the substrates 1 to 4 produced in Examples 1and 2 and Comparative Examples 1 and 2 are shown in Table 4. TABLE 4Contact angle of the treated surface Water After surface n-octanen-hexane Substrate Initial abrasion Initial Initial Example 1  72.5 deg.— — — Comparative Example 1  97.7 deg. —   0 deg. — Example 2 114.0 deg.112.0 deg. 47.2 deg. 63.8 deg. Comparative Example 2 111.2 deg. 100.7deg. — —

Example 3

[0140] A surface layer of 100 nm thick was formed on the Substrate 1 ofExample 1 by sputtering using a SiO₂ target after treating the surfaceof the inner layer for surface modification by sputter etching to ensuregood adhesion between the inner layer and the surface layer at theirboundary (Substrate 11).

[0141] The substrate was then evaluated for its abrasion resistance byTaber abrasion test by repeating the procedure of Example 1. The hazevalues (ΔHaze, %) after 100 and 500 abrasion rotations were 0.6% and2.2%, respectively, confirming the markedly improved scratch resistanceof this substrate even when compared to Example 1.

Comparative Example 3

[0142] A surface layer of 100 nm thick was formed on the Substrate 2 ofComparative Example 1 by sputtering using a SiO₂ target after treatingthe surface of the inner layer (Substrate 12).

[0143] The substrate was then evaluated for its abrasion resistance byTaber abrasion test by repeating the procedure of Example 1. The hazevalues (ΔHaze, %) after 100 and 500 abrasion rotations were 9.3% and32.4%, respectively, indicating no substantial improvement overComparative Example 1 which exhibited inferior scratch resistancecompared to that of the Examples 1 and 3.

[0144] The results of Examples 1 and 3 and Comparative Examples 1 and 3demonstrate the merits of the present invention realized by theprovision of the surface SiO₂ layer formed by sputtering.

[0145] The haze values (ΔHaze, %) of Substrates 1, 2, 11 and 12 ofExamples 1 and 3 and Comparative Examples 1 and 3 after the abrasiontest are shown in Table 5. TABLE 5 ΔHaze (%) in abrasion test Substrateafter 100 rotations after 500 rotations Example 1 2.0 5.3 Example 3 0.62.2 Comparative Example 1 14.0 36.2 Comparative 9.3 32.4 Example 3

Example 4

[0146] In a DVD-RAM (recording capacity, 2.6 GByte/face) having apolycarbonate substrate which is not covered with a protective coatingon side of the light incidence, the surface of the substrate on the sideof the light incidence was spin coated with a UV-curable resin admixedwith silica particles (DeSolite Z7503 manufactured by JSR Co., Ltd.).The coated film was heated in air at 60° C. for 3 minutes for thesolvent removal, and cured by UV irradiation (high pressure mercurylamp, 550 mJ/cm²). The cured film had a thickness of about 3.4 μm. Thethus treated surface was spin coated with 0.1% (mass %) perfluorchexanesolution of DSX (manufactured by Daikin Industries, Ltd.) which is awater- and oil-repellent silane coupling agent within the scope offormula (1), and the sample was heated in atmosphere at 60° C. for 10hours for chemisorption (Medium 1). The film of the silane couplingagent had a thickness of about 10 nm.

[0147] Next, the disk was recorded in the area of from 39.5 to 57.5 mmin diameter with a random signal to measure the bit error rate (BER) inthe recording. Average value of the bit error rate in the entirerecording area was 4.4×10⁻⁵. Fingerprints were then attached on theentire recording area of the disk, and attempts were made to read thedisk. The disk was unreadable. The disk was then wiped in radialdirection from its inner periphery to its outer periphery with BemcotLint Free CT-8 (manufactured by Asahi Chemical Industry Co., Ltd.) at apressure of 100±10 g/cm² for 20 times to thereby wipe off thefingerprints on the disk. After wiping off the fingerprints, the diskwas overwritten with a random signal and read. The −4 average value ofBER was 2.2×10⁻⁴, and reading at an error rate similar to that of theinitial state was possible. It was thus confirmed that the resistance toorganic contaminants can be markedly increased by treating the disksurface with a water-and oil-repellent coupling agent. The results areshown in FIG. 3. The treated surface also exhibited excellent scratchresistance. It should be noted that the recording/reading beam wasirradiated from the side of the silane coupling agent film formed on thesubstrate with the intervening resin layer.

Comparative Example 4

[0148] In a DVD-RAM (recording capacity, 2.6 GByte/face) having apolycarbonate substrate which is not covered with a protective coatingon side of the light incidence, the surface of the substrate on the sideof the light incidence was spin coated with a UV-curable acrylic resin(HOD-3091 manufactured by Nippon Kayaku Co., Ltd.), and the coated filmwas cured by UV 2 irradiation (high pressure mercury lamp, 550 mJ/cm²).The cured film had a thickness of about 3.3 μm (Medium 2).

[0149] Next, the disk was recorded in the area of from 39.5 to 57.5 mmin diameter with a random signal to measure the bit error rate (BER) inthe recording. Average value of the bit error rate was 2.2×10⁻⁵.Fingerprints were then attached on the entire recording area of thedisk, and attempts were made to read the disk. The disk was unreadableas in the case of the medium 1. The disk was then wiped in radialdirection from its inner periphery to its outer periphery with BemcotLint Free CT-8 (manufactured by Asahi Chemical Industry Co., Ltd.) at apressure of 100±10 g/cm² for 20 times to thereby wipe off thefingerprints on the disk. After wiping off the fingerprints, the diskwas overwritten with a random signal and read. The average value of BERwas 7.8×10⁻³ indicating significant deterioration compared to theinitial state. In other words, the fingerprints could not be completelyremoved in the case of the hard coat formed by using the conventionalUV-curable resin, and the hard coat was not at all smudge proof. Theresults are also shown in FIG. 3. The treated surface also exhibitedinferior scratch resistance compared to the medium 1. It should be notedthat the recording/reading beam was irradiated from the side of theresin layer formed on the substrate.

Example 5

[0150] In Example 4, a film of DeSolite Z7503 (manufactured by JSR Co.,Ltd.) was formed on the surface of the substrate of the DVD-RAM on theside of the light incidence. The cured film had a thickness of 3.4 μm.The surface was then treated for surface modification by repeating theprocedure of Example 3, and a SiO₂ layer was formed to a thickness of100 nm by sputtering. On the SiO₂ layer was formed a film of silanecoupling agent to a thickness of about 10 nm by repeating the procedureof Example 4 (Medium 11) This disk exhibited smudge proof propertiesequivalent to those of Example 4, and the scratch resistance was furtherimproved over that of Example 4 in correspondence with the results ofExample 3.

Example 6

[0151] In a magneto-optical disk having no protective coating on thepolycarbonate substrate and having a protective coating of a UV-curedacrylic resin as the outermost layer on the side of the recording layer,the substrate surface and the surface of the protective coating on theside of the recording layer were respectively formed with a layer ofUV-curable resin admixed with the silica particles by repeating theprocedure of Example 3, and then, a film of silane coupling agent(Medium 3).

[0152] The thus produced medium 3 was found to exhibit excellentabrasion resistance as well as excellent smudge proof properties.

[0153] When the recording and the reading of the disk was conducted byirradiating the disk from the side of the substrate and moving themagnetic head in contact with the silane coupling agent film formed onthe side of the protective coating of the recording layer, it was foundthat the treated disk surface functions as a lubrication film in themoving of the magnetic head to result in good moving properties as wellas excellent durability.

Merits of the Invention

[0154] As described above, the present invention provides an opticalinformation medium which has excellent scratch resistance. The presentinvention also enables sufficient smudge-proof properties (inparticular, easy removal of the contaminant) to be retained for aprolonged period. Therefore, the optical information medium such as anoptical disk does not suffer from serious contamination problem when itis used without being accommodated in a cartridge, shell, or caddy.

[0155] Japanese Patent Application Nos. 107681/2000, 309218/2000 and068761/2001 are incorporated herein by reference.

[0156] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in the light of theabove teachings. It is therefore to be understood that, within the scopeof the appended claims, the invention may be practiced otherwise than asspecifically described.

1. An optical information medium to be optically recorded and/or read,wherein said medium is coated on at least one surface with a film of asilane coupling agent containing a water- or oil-repellent substituent,said silane coupling agent being represented by the following formula(1): R₁—Si(X)(Y)(Z)  (1) wherein R₁ is the water- or oil-repellentsubstituent; X, Y and Z are independently a monovalent group; and atleast one of X, Y and Z is a group which is capable of forming Si—O—Sibond by polycondensation with silanol group; and said medium has anunderlying layer formed in contact with said silane coupling agent film,and at least the surface of said underlying layer comprises a compoundhaving a chemical bond represented by the formula (2): M—A  (2) whereinM is a metal atom (including a semimetal), and A is a chalcogen atomselected from O, S, Se, and Te, nitrogen atom, or carbon atom.
 2. Anoptical information medium according to claim 1 wherein the surface ofthe underlying layer coated with said silane coupling agent comprises anactive energy beam-curable resin containing a metal (includingsemimetal) chalcogenide particle, and said metal chalcogenide particlehas an average particle size of up to 500 nm.
 3. An optical informationmedium to be optically recorded and/or read, wherein said medium iscoated on at least one surface with a film of a silane coupling agentcontaining a water- or oil-repellent substituent, said silane couplingagent being represented by the following formula (1):R₁—Si(X)(Y)(Z)  (1) wherein R₁ is the water- or oil-repellentsubstituent; X, Y and Z are independently a monovalent group; and atleast one of X, Y and Z is a group which is capable of forming Si—O—Sibond by polycondensation with silanol group; and said medium has anunderlying layer formed in contact with said silane coupling agent film,and said underlying layer has a surface comprising a thin layer of ametal (including a semimetal) compound having a thickness of up to 1 μmformed in contact with said silane coupling agent film, and a metal(including a semimetal) compound-containing layer having a thicknessthicker than said thin layer is formed in contact with said thin layerand on the side opposite to said silane coupling agent film.
 4. Anoptical information medium according to claim 3 wherein said metal(including a semimetal) compound-containing layer formed in contact withsaid thin layer comprises an active energy beam-curable resin containingparticles of a metal compound selected from a metal (includingsemimetal) chalcogenide, a metal (including semimetal) nitride, and ametal (including semimetal) carbide; and said metal compound particlehas an average particle size of up to 500 nm.
 5. An optical informationmedium according to claim 3 wherein said metal (including a semimetal)compound-containing layer formed in contact with said thin layercomprises a composition containing a hydrolyzable metal (includingsemimetal) compound.
 6. An optical information medium according to claim3 wherein said metal (including a semimetal) compound-containing layerformed in contact with said thin layer comprises a compound containing apoylsilazane.
 7. An optical information medium according to any one ofclaims 1 to 6 wherein the substituent R₁ in formula (1) is a water- oroil-repellent fluorohydrocarbon substituent.
 8. An optical informationmedium according to any one of claims 1 to 7 wherein at least one of X,Y and Z in formula (1) is selected from a halogen, —OH, —OR₂ (wherein R₂is an alkyl group), —OC(O)CH₃, —NH₂ and —N═C═O.
 9. An opticalinformation medium according to any one of claims 1 to 8 wherein saidmedium has a supporting substrate, and the recording and/or the readingis accomplished by irradiating a light beam from the side of saidsupporting substrate, and said silane coupling agent film is formed onthe side of the light beam incidence.
 10. An optical information mediumaccording to claim 9 wherein said optical information medium is amagneto-optical disk used by magnetic field modulation process which hasa recording layer formed on the supporting substrate, wherein therecording and the reading is accomplished by irradiating a light beamfrom the side of said supporting substrate, and wherein a magnetic headis run on the side of said recording layer, and said disk is coated withsaid silane coupling agent film on both the side of the light beamincidence and the side of the magnetic head.
 11. An optical informationmedium comprising a supporting substrate and a film layer formed on thesupporting substrate to be optically recorded and/or read by a lightbeam irradiated from the side of said supporting substrate or said filmlayer, wherein said medium is coated on the side of the light incidencewith a thin layer having a thickness of up to 1 μm comprising a metal(including a semimetal) compound selected from a metal (includingsemimetal) chalcogenide, a metal (including semimetal) nitride, and ametal (including semimetal) carbide, and a metal (including a semimetal)compound-containing layer having a thickness thicker than said thinlayer is formed in contact with said thin layer and on the side oppositeto the side of the light incidence.
 12. An optical information mediumcomprising a supporting substrate and a film layer formed on thesupporting substrate to be optically recorded and/or read by a lightirradiated from the side of said supporting substrate or said filmlayer, wherein said medium is coated on the side of the light incidencewith a thin layer having a thickness of up to 1 μm comprising hardcarbon (diamond like carbon), and a metal (including a semimetal)compound-containing layer having a thickness thicker than said thinlayer formed in contact with said thin layer and on the side opposite tothe side of the light incidence.
 13. An optical information mediumaccording to claim 11 or 12 wherein said metal (including a semimetal)compound-containing layer formed in contact with said thin layercomprises an active energy beam-curable resin containing particles of ametal compound selected from a metal (including semimetal) chalcogenide,a metal (including semimetal) nitride, and a metal (including semimetal)carbide; and said metal compound particle has an average particle sizeof up to 500 nm.
 14. An optical information medium according to claim 11or 12 wherein said metal (including a semimetal) compound-containinglayer formed in contact with said thin layer comprises a compositioncontaining a hydrolyzable metal (including semimetal) compound.
 15. Anoptical information medium according to claim 11 or 12 wherein saidmetal (including a semimetal) compound-containing layer formed incontact with said thin layer comprises a compound containing apolysilazane.
 16. An optical information medium comprising a supportingsubstrate and a film layer formed on the supporting substrate which isoptically recorded and/or read by irradiating a light beam from the sideof said supporting substrate or said film layer, wherein said medium isformed on the side of the light incidence with a light-transmittinglayer; and at least a part of said light-transmitting layer comprises anactive energy beam-curable resin containing particles of a metalcompound selected from a metal (including semimetal) chalcogenide, ametal (including semimetal) nitride, and a metal (including semimetal)carbide; and said metal compound particle has an average particle sizeof up to 500 nm.
 17. An optical information medium according to any oneof claim 4 , 13 , or 16 wherein said metal compound particle is a metalchalcogenide particle.
 18. An optical information medium according toany one of claim 2 , 4 , 13, or 17 wherein said metal chalcogenideparticle is silica particle.